Decrement Evoked Potential Mapping: Basis of a Mechanistic Strategy for Ventricular Tachycardia Ablation

Catheter Ablation of Ventricular Tachycardia in Ischemic Heart Disease: What Is Known and New Perspectives

PURPOSE OF THE REVIEW

This review aims to evaluate current evidence regarding ventricular tachycardia ablation in patients with ischemic heart disease and explore novel approaches currently developing to improve procedural and long-term outcomes.

RECENT FINDINGS

Recently published trials (PARTITA, PAUSE-SCD, and SURVIVE-VT) have demonstrated the prognostic benefit of prophylactic ventricular tachycardia ablation compared to current clinical practice. Advanced cardiac imaging provides a valuable pre-procedural evaluation of the arrhythmogenic substrate, identifying ablation targets non-invasively. Advanced cardiac mapping techniques allow to better characterize arrhythmogenic substrate during ablation procedure. Emerging technologies like pulsed field ablation and ultra-low temperature cryoablation show promise in ventricular tachycardia ablation. Advancements in mapping techniques, ablation technologies, and pre-procedural cardiac imaging offer promise for improving ventricular tachycardia ablation outcomes in ischemic heart disease.

Substrate Mapping for Ventricular Tachycardia Ablation Through High-Density Whole-Chamber Double Extra Stimuli: The S3 Protocol

BACKGROUND

A partial delineation of targets for ablation of ventricular tachycardia (VT) during a stable rhythm is likely responsible for a suboptimal success rate. The abnormal low-voltage near-field functional components may be hidden within the high-amplitude far-field signal.

OBJECTIVES

The aim of this study was to evaluate the benefit and feasibility of functional substrate mapping using a full-ventricle S3 protocol and to assess its colocalization with arrhythmogenic conducting channels (CCs) on late gadolinium enhancement cardiac magnetic resonance.

METHODS

An S3 mapping protocol with a drive train of S1 followed by S2 (effective refractory period + 30 ms) and S3 (effective refractory period + 50 ms) from the right ventricular apex was performed in 40 consecutive patients undergoing scar-related VT ablation. Deceleration zones (DZs) and areas of late potentials (LPs) were identified for all maps. A preprocedural noninvasive substrate assessment was done using late gadolinium enhancement cardiac magnetic resonance and postprocessing with automated CC identification.

RESULTS

The S3 protocol was completed in 34 of the 40 procedures (85.0%). The S3 protocol enhanced the identification of VT isthmus on the basis of DZ (89% vs 62%; P < 0.01) and LP (93% vs 78%; P = 0.04) assessment. The percentage of CCs unmasked by DZs and LPs using S3 maps was significantly higher than the ones using S2 and S1 maps (78%, 65%, and 48% [P < 0.001] and 88%, 81%, and 68% [P < 0.01], respectively). The functional substrate identified during S3 activation mapping was significantly more extensive than the one identified using S2 and S1, including a greater number of DZs (2.94, 2.47, and 1.82, respectively; P < 0.001) and a wider area of LPs (44.1, 38.2, and 29.4 cm2, respectively; P < 0.001). After VT ablation, 77.9% of patients have been VT free during a median follow-up period of 13.6 months.

CONCLUSIONS

The S3 protocol was feasible in 85% of patients, allows a better identification of targets for ablation, and might improve VT ablation results.

Ventricular Tachycardia Ablation Endpoints: Moving Beyond Noninducibility

In patients with structural heart disease and ventricular tachycardia (VT) undergoing catheter ablation, the response to programmed electrical stimulation (PES) at the end of the procedure has been traditionally used to evaluate the acute success and predict long-term outcomes. Although noninducibility at PES has been extensively investigated and validated in clinical trials and large multicenter registries, its performance in predicting long-term freedom from VT is suboptimal. In addition, PES has inherent limitations related to the influence of background antiarrhythmic drug therapy, periprocedural use of anesthesia, and the heterogeneity in PES protocols. The increased utilization of substrate-based ablation approaches that focus on ablation of abnormal electrograms identified with mapping in sinus or paced rhythm has been paralleled by a need for additional procedural endpoints beyond VT noninducibility at PES. This article critically appraises the relative merits and limitations of different procedural endpoints according to different ablation techniques for catheter ablation of scar-related VT.

Non-invasive detection of slow conduction with cardiac magnetic resonance imaging for ventricular tachycardia ablation

AIMS

Non-invasive myocardial scar characterization with cardiac magnetic resonance (CMR) has been shown to accurately identify conduction channels and can be an important aid for ventricular tachycardia (VT) ablation. A new mapping method based on targeting deceleration zones (DZs) has become one of the most commonly used strategies for VT ablation procedures. The aim of the study was to analyse the capability of CMR to identify DZs and to find predictors of arrhythmogenicity in CMR channels.

METHODS AND RESULTS

Forty-four consecutive patients with structural heart disease and VT undergoing ablation after CMR at a single centre (October 2018 to July 2021) were included (mean age, 64.8 ± 11.6 years; 95.5% male; 70.5% with ischaemic heart disease; a mean ejection fraction of 32.3 ± 7.8%). The characteristics of CMR channels were analysed, and correlations with DZs detected during isochronal late activation mapping in both baseline maps and remaps were determined. Overall, 109 automatically detected CMR channels were analysed (2.48 ± 1.15 per patient; length, 57.91 ± 63.07 mm; conducting channel mass, 2.06 ± 2.67 g; protectedness, 21.44 ± 25.39 mm). Overall, 76.1% of CMR channels were associated with a DZ. A univariate analysis showed that channels associated with DZs were longer [67.81 ± 68.45 vs. 26.31 ± 21.25 mm, odds ratio (OR) 1.03, P = 0.010], with a higher border zone (BZ) mass (2.41 ± 2.91 vs. 0.87 ± 0.86 g, OR 2.46, P = 0.011) and greater protectedness (24.97 ± 27.72 vs. 10.19 ± 9.52 mm, OR 1.08, P = 0.021).

CONCLUSION

Non-invasive detection of targets for VT ablation is possible with CMR. Deceleration zones found during electroanatomical mapping accurately correlate with CMR channels, especially those with increased length, BZ mass, and protectedness.

Management of ventricular tachycardias: insights on centre settings, procedural workflow, endpoints, and implementation of guidelines-results from an EHRA survey

Ventricular tachycardia (VT), and its occurrence, is still one of the main reasons for sudden cardiac death and, therefore, for increased mortality and morbidity foremost in patients with structural heart [Kahle A-K, Jungen C, Alken F-A, Scherschel K, Willems S, Pürerfellner H et al. Management of ventricular tachycardia in patients with ischaemic cardiomyopathy: contemporary armamentarium. Europace 2022;24:538-51]. Catheter ablation has become a safe and effective treatment option in patients with recurrent VT [Cronin EM, Bogun FM, Maury P, Peichl P, Chen M, Namboodiri N et al. 2019 HRS/EHRA/APHRS/LAHRS expert consensus statement on catheter ablation of ventricular arrhythmias. Heart Rhythm 2020;17:e2-154]. Previous and current guidelines provide guidance on indication for VT ablation and risk assessment and evaluation of underlying disease. However, no uniform recommendation is provided regarding procedural strategies, timing of ablation, and centre setting. Therefore, these specifics seem to differ largely, and recent data are sparse. This physician-based European Heart Rhythm Association survey aims to deliver insights on not only infrastructural settings but also procedural specifics, applied technologies, ablation strategies, and procedural endpoints. Therefore, these findings might deliver a real-world scenario of VT management and potentially are of guidance for other centres.

Identification of Human Ventricular Tachycardia Demarcated by Fixed Lines of Conduction Block in a 3-Dimensional Hyperboloid Circuit

BACKGROUND

The circuit boundaries for reentrant ventricular tachycardia (VT) have been historically conceptualized within a 2-dimensional (2D) construct, with their fixed or functional nature unresolved. This study aimed to examine the correlation between localized lines of conduction block (LOB) evident during baseline rhythm with lateral isthmus boundaries that 3-dimensionally constrain the VT isthmus as a hyperboloid structure.

METHODS

A total of 175 VT activation maps were correlated with isochronal late activation maps during baseline rhythm in 106 patients who underwent catheter ablation for scar-related VT from 3 centers (42% nonischemic cardiomyopathy). An overt LOB was defined by a deceleration zone with split potentials (≥20 ms isoelectric segment) during baseline rhythm. A novel application of pacing within deceleration zone (≥600 ms) was implemented to unmask a concealed LOB not evident during baseline rhythm. LOB identified during baseline rhythm or pacing were correlated with isthmus boundaries during VT.

RESULTS

Among 202 deceleration zones analyzed during baseline rhythm, an overt LOB was evident in 47%. When differential pacing was performed in 38 deceleration zones without overt LOB, an underlying concealed LOB was exposed in 84%. In 152 VT activation maps (2D=53, 3-dimensional [3D]=99), 69% of lateral boundaries colocalized with an LOB in 2D activation patterns, and the depth boundary during 3D VT colocalized with an LOB in 79%. In VT circuits with isthmus regions that colocalized with a U-shaped LOB (n=28), the boundary invariably served as both lateral boundaries in 2D and 3D. Overall, 74% of isthmus boundaries were identifiable as fixed LOB during baseline rhythm or differential pacing.

CONCLUSIONS

The majority of VT circuit boundaries can be identified as fixed LOB from intrinsic or paced activation during sinus rhythm. Analysis of activation while pacing within the scar substrate is a novel technique that may unmask concealed LOB, previously interpreted to be functional in nature. An LOB from the perspective of a myocardial surface is frequently associated with intramural conduction, supporting the existence of a 3D hyperboloid VT circuit structure. Catheter ablation may be simplified to targeting both sides around an identified LOB during sinus rhythm.

Ablation targets of scar-related ventricular tachycardia identified by dynamic functional substrate mapping

BACKGROUND

Dynamic functional substrate mapping of scar-related ventricular tachycardia offers better identification of ablation targets with limited ablation lesions. Several functional substrate mapping approaches have been proposed, including decrement-evoked potential (DEEP) mapping. The aim of our study was to compare the short- and long-term efficacy of a DEEP-guided versus a fixed-substrate-guided strategy for the ablation of scar-related ventricular tachycardia (VT).

RESULTS

Forty consecutive patients presenting for ablation of scar-related VT were randomized to either DEEP-guided or substrate-guided ablation. Late potentials were tagged and ablated in the non-DEEP group, while those in the DEEP group were subjected to RV extrastimulation after a drive train. Only potentials showing significant delay were ablated. Patients were followed for a median duration of 12 months. Twenty patients were allocated to the DEEP group, while the other 20 were allocated to the non-DEEP group. Twelve patients (60%) in the DEEP group had ischemic cardiomyopathy versus 10 patients (50%) in the non-DEEP group (P-value 0.525). Intraoperatively, the median percentage of points with LPs was 19% in the DEEP group and 20.6% in the non-DEEP group. The procedural time was longer in the DEEP group, approaching but missing statistical significance (P-value 0.059). VT non-inducibility was successfully accomplished in 16 patients (80%) in the DEEP group versus 17 patients (85%) in the non-DEEP group (P value 0.597). After a median follow-up duration of 12 months, the VT recurrence rate was 65% in both groups (P value 0.311), with a dropout rate of 10% in the DEEP group. As for the secondary endpoints, all-cause mortality rates were 20% and 25% in the DEEP and non-DEEP groups, respectively (P-value 0.342).

CONCLUSIONS

DEEP-assisted ablation of scar-related ventricular tachycardia is a feasible strategy with comparable short- and long-term outcomes to a fixed-substrate-based strategy with more specific ablation targets, albeit relatively longer but non-significant procedural times and higher procedural deaths. The imbalance between the study groups in terms of epicardial versus endocardial mapping, although non-significant, warrants the prudent interpretation of our results. Further large-scale randomized trials are recommended.

TRIAL REGISTRATION

clinicaltrials.gov, registration number: NCT05086510, registered on 28th September 2021, record https://classic.

CLINICALTRIALS

gov/ct2/show/NCT05086510.

Decrement Evoked Potential (DEEP) Mapping of the Atria: Unmasking Atrial Fibrillation Substrate

BACKGROUND

Atrial myopathy may underlie the progression of atrial fibrillation (AF) from a treatable disease to an irreversible condition with poor ablation outcomes. Electrophysiological methods to unmask areas prone to re-entry initiation could be key to defining latent atrial myopathy.

METHODS

Consecutive patients referred for AF ablation were prospectively included at four institutions. Decrement evoked potential mapping (DEEP) was performed in eight left atrial sites and five right atrial sites, from two different pacing locations (endocardially from the left atrial appendage, epicardially from the proximal coronary sinus). The electrograms (EGMs) during S1 600 ms drive and after an extra stimulus (S2 at +30 ms above atrial refractoriness) were studied at each location and assessed for decremental properties. Follow-up was 12 months.

RESULTS

Seventy-four patients were included and 85% had persistent AF. A total of 17,614 EGMs were individually analysed and measured. Nine percent of the EGMs showed DEEP properties (local delay of >10 ms after S2) with a mean decrement of 33±26 ms. DEEPs were more frequent in the left atrium than the right atrium (9.4% vs 8.0%; p<0.001) and more prevalent in persistent AF patients than paroxysmal AF patients (9.8% vs 4.6% p=0.001). Atrial DEEPs were more frequently unmasked in normal bipolar voltage areas and by epicardial pacing than endocardial pacing (9.6% vs 8.4%, respectively; p=0.004). Within the left atrium, the roof had the highest prevalence of DEEP EGMs.

CONCLUSIONS

DEEP mapping of both atria is useful for highlighting areas with a tendency for unidirectional block and re-entry initiation. Those areas are more easily unmasked by epicardial pacing from the coronary sinus and more prevalent in persistent AF patients than in paroxysmal AF patients.

Innovations in ventricular tachycardia ablation

Catheter ablation of ventricular arrhythmias (VAs) has evolved significantly over the past decade and is currently a well-established therapeutic option. Technological advances and improved understanding of VA mechanisms have led to tremendous innovations in VA ablation. The purpose of this review article is to provide an overview of current innovations in VA ablation. Mapping techniques, such as ultra-high density mapping, isochronal late activation mapping, and ripple mapping, have provided improved arrhythmogenic substrate delineation and potential procedural success while limiting duration of ablation procedure and potential hemodynamic compromise. Besides, more advanced mapping and ablation techniques such as epicardial and intramyocardial ablation approaches have allowed operators to more precisely target arrhythmogenic substrate. Moreover, advances in alternate energy sources, such as electroporation, as well as stereotactic radiation therapy have been proposed to be effective and safe. New catheters, such as the lattice and the saline-enhanced radiofrequency catheters, have been designed to provide deeper and more durable tissue ablation lesions compared to conventional catheters. Contact force optimization and baseline impedance modulation are important tools to optimize VT radiofrequency ablation and improve procedural success. Furthermore, advances in cardiac imaging, specifically cardiac MRI, have great potential in identifying arrhythmogenic substrate and evaluating ablation success. Overall, VA ablation has undergone significant advances over the past years. Innovations in VA mapping techniques, alternate energy source, new catheters, and utilization of cardiac imaging have great potential to improve overall procedural safety, hemodynamic stability, and procedural success.

Association of Sinus Wavefront Activation and Ventricular Extrastimuli Mapping With Ventricular Tachycardia Re-Entrant Circuits

BACKGROUND

Substrate-based ablation targets areas of delayed and fractionated electrograms during sinus rhythm, which are sensitive for identifying the ventricular tachycardia (VT) isthmus but is influenced by the activation wavefront direction and decremental pacing.

OBJECTIVES

The aim of this study was to correlate the areas of latest activation during varying wavefront activation mapping and decremental pacing mapping with sites critical to the VT isthmus.

METHODS

Three high-density electroanatomical substrate maps were created in patients presenting for ablation of monomorphic VT: 1) native sinus rhythm; 2) right ventricular (RV) apical pacing; and 3) an RV apical S2 map following the S1 drive train at 20 ms above the ventricular effective refractory period. Areas corresponding to the latest activation were compared with the VT isthmus identified by conventional mapping.

RESULTS

Twenty patients with structural heart disease with a mean age of 55.6 ± 16.9 years were included. The majority of the cohort consisted of patients with ischemic heart disease (50%) and arrhythmogenic RV cardiomyopathy (35%). Epicardial ablation was performed in 45% of patients. The concordance of the site of latest activation in sinus rhythm with the VT isthmus was 75%. The location of the latest activation during RV apical pacing corresponded with the VT isthmus in 85% of cases. However, in 95% of cases, the site of the latest activation following the S2 stimulus colocalized to the VT isthmus.

CONCLUSIONS

In a mix of underlying myocardial substrates, regions of conduction slowing during decremental pacing colocalize with the VT isthmus more frequently than sinus rhythm activation mapping and may have a role in substrate-based ablation where VT induction is undesirable.

Impact of electrode orientation, myocardial wall thickness, and myofiber direction on intracardiac electrograms: numerical modeling and analytical solutions

Intracardiac electrograms (iEGMs) are time traces of the electrical potential recorded close to the heart muscle. We calculate unipolar and bipolar iEGMs analytically for a myocardial slab with parallel myofibers and validate them against numerical bidomain simulations. The analytical solution obtained via the method of mirrors is an infinite series of arctangents. It goes beyond the solid angle theory and is in good agreement with the simulations, even though bath loading effects were not accounted for in the analytical calculation. At a large distance from the myocardium, iEGMs decay as 1/R (unipolar), 1/R ² (bipolar and parallel), and 1/R ³ (bipolar and perpendicular to the endocardium). At the endocardial surface, there is a mathematical branch cut. Here, we show how a thicker myocardium generates iEGMs with larger amplitudes and how anisotropy affects the iEGM width and amplitude. If only the leading-order term of our expansion is retained, it can be determined how the conductivities of the bath, torso, myocardium, and myofiber direction together determine the iEGM amplitude. Our results will be useful in the quantitative interpretation of iEGMs, the selection of thresholds to characterize viable tissues, and for future inferences of tissue parameters.

Lateral Boundaries of the Ventricular Tachycardia Circuit Align With Sinus Rhythm Discontinuities

BACKGROUND

Sinus rhythm electrical activation mapping can provide information regarding the ischemic re-entrant ventricular tachycardia (VT) circuit. The information gleaned may include the localization of sinus rhythm electrical discontinuities, which can be defined as arcs of disrupted electrical conduction with large activation time differences across the arc.

OBJECTIVES

This study sought to detect and localize sinus rhythm electrical discontinuities that might be present in activation maps constructed from infarct border zone electrograms.

METHODS

Monomorphic re-entrant VT with a double-loop circuit and central isthmus was repeatedly inducible by programmed electrical stimulation in the epicardial border zone of 23 postinfarction canine hearts. Sinus rhythm and VT activation maps were constructed from 196 to 312 bipolar electrograms acquired surgically at the epicardial surface and analyzed computationally. A complete re-entrant circuit was mappable from the epicardial electrograms of VT, and isthmus lateral boundary (ILB) locations were ascertained. The difference in sinus rhythm activation time across ILB locations, vs the central isthmus and vs the circuit periphery, was determined.

RESULTS

Sinus rhythm activation time differences averaged 14.4 milliseconds across the ILB vs 6.5 milliseconds at the central isthmus and 6.4 milliseconds at the periphery (ie, the outer circuit loop) (P ≤ 0.001). Locations with large sinus rhythm activation difference tended to overlap ILB (60.3% ± 23.2%) compared with their overlap with the entire grid (27.5% ± 18.5%) (P < 0.001).

CONCLUSIONS

Disrupted electrical conduction is evident as discontinuity in sinus rhythm activation maps, particularly at ILB locations. These areas may represent permanent fixtures relating to spatial differences in border zone electrical properties, caused in part by alterations in underlying infarct depth. The tissue properties producing sinus rhythm discontinuity at ILB may contribute to functional conduction block formation at VT onset.

Computer-aided detection of arrhythmogenic sites in post-ischemic ventricular tachycardia

Nowadays, catheter-based ablation in patients with post-ischemic ventricular tachycardia (VT) is performed in arrhythmogenic sites identified by electrophysiologists by visual inspection during electroanatomic mapping. This work aims to present the development of machine learning tools aiming at supporting clinicians in the identification of arrhythmogenic sites by exploiting innovative features that belong to different domains. This study included 1584 bipolar electrograms from nine patients affected by post-ischemic VT. Different features were extracted in the time, time scale, frequency, and spatial domains and used to train different supervised classifiers. Classification results showed high performance, revealing robustness across the different classifiers in terms of accuracy, true positive, and false positive rates. The combination of multi-domain features with the ensemble tree is the most effective solution, exhibiting accuracies above 93% in the 10-time 10-fold cross-validation and 84% in the leave-one-subject-out validation. Results confirmed the effectiveness of the proposed features and their potential use in a computer-aided system for the detection of arrhythmogenic sites. This work demonstrates for the first time the usefulness of supervised machine learning for the detection of arrhythmogenic sites in post-ischemic VT patients, thus enabling the development of computer-aided systems to reduce operator dependence and errors, thereby possibly improving clinical outcomes.

Ripple mapping in ventricular tachycardia substrate mapping and ablation of nonischemic ventricular tachycardia

INTRODUCTION

Substrate-based ablation for ventricular tachycardia (VT) using Ripple map (RM) is an effective treatment strategy for patients with ischemic cardiomyopathy but has yet to be evaluated in patients with nonischemic cardiomyopathy (NICMO). The aim of this study is to determine the feasibility and effectiveness of an RM-based ablation for NICMO patients.

METHODS AND RESULTS

This was a single-center, retrospective study including all NICMO patients undergoing VT ablation at St Vincent Hospital between January 1, 2018 and January 12, 2019. Retrospective RM analysis was performed on those that had a substrate-based ablation to identify the location and number of Ripple channels as well as their proximity to ablation lesions. Thirty-three patients met the inclusion criteria and had a median age of 65 (58, 73.5) with 15.2% of the population being female, and were followed for a median duration of 451 (217.5, 586.5) days. Of these patients, 23 (69.7%) had a substrate-based ablation with a median procedural duration of 196.4 (186.8, 339) min, 1946 (517, 2750) points collected per map, and 277 (141, 554) points were within the scar. Two (8.6%) procedural complications occurred, and 7 (30.4%) patients had VT recurrence during follow-up. RM analysis revealed an average of two Ripple channels and the patients without VT recurrence had ablation performed closer to the Ripple channels: 0 (0, 4.7) versus 14.3 (0, 23.5) cm; p = .02.

CONCLUSION

An RM-based substrate ablation can be performed in NICMO patients and ablation within Ripple channels is a predictor of VT freedom.

The value of functional substrate mapping in ventricular tachycardia ablation

In the setting of structural heart disease, ventricular tachycardia (VT) is typically associated with a re-entrant mechanism. In patients with hemodynamically tolerated VTs, activation and entrainment mapping remain the gold standard for the identification of the critical parts of the circuit. However, this is rarely accomplished, as most VTs are not hemodynamically tolerated to permit mapping during tachycardia. Other limitations include noninducibility of arrhythmia or nonsustained VT. This has led to the development of substrate mapping techniques during sinus rhythm, eliminating the need for prolonged periods of mapping during tachycardia. Recurrence rates following VT ablation are high; therefore, new mapping techniques for substrate characterization are required. Advances in catheter technology and especially multielectrode mapping of abnormal electrograms has increased the ability to identify the mechanism of scar-related VT. Several substrate-guided approaches have been developed to overcome this, including scar homogenization and late potential mapping. Dynamic substrate changes are mainly identified within regions of myocardial scar and can be identified as local abnormal ventricular activities. Furthermore, mapping strategies incorporating ventricular extrastimulation, including from different directions and coupling intervals, have been shown to increase the accuracy of substrate mapping. The implementation of extrastimulus substrate mapping and automated annotation require less extensive ablation and would make VT ablation procedures less cumbersome and accessible to more patients.

Retrospective Window of Interest Annotation Provides New Insights Into Functional Channels in Ventricular Tachycardia Substrate

BACKGROUND

Accurate annotation of local activation time is crucial in the functional assessment of ventricular tachycardia (VT) substrate. A major limitation of modern mapping systems is the standard prospective window of interest (sWOI) is limited to 490 to 500 milliseconds, preventing annotation of very late potentials (LPs). A novel retrospective window of interest (rWOI), which allows annotation of all diastolic potentials, was used to assess the functional VT substrate.

OBJECTIVES

This study sought to investigate the utility of a novel rWOI, which allows accurate visualization and annotation of all LPs during VT substrate mapping.

METHODS

Patients with high-density VT substrate maps and a defined isthmus were included. All electrograms were manually annotated to latest activation using a novel rWOI. Reannotated substrate maps were correlated to critical sites, with areas of late activation examined. Propagation patterns were examined to assess the functional aspects of the VT substrate.

RESULTS

Forty-eight cases were identified with 1,820 ± 826 points per map. Using the novel rWOI, 31 maps (65%) demonstrated LPs beyond the sWOI limit. Two distinct patterns of channel activation were seen during substrate mapping: 1) functional block with unidirectional conduction into the channel (76%); and 2) wave front collision within the channel (24%). In addition, a novel marker termed the zone of early and late crowding was studied in the rWOI substrate maps and found to have a higher positive predictive value (85%) than traditional deceleration zones (69%) for detecting critical sites of re-entry.

CONCLUSIONS

The standard WOI of contemporary mapping systems is arbitrarily limited and results in important very late potentials being excluded from annotation. Future versions of electroanatomical mapping systems should provide longer WOIs for accurate local activation time annotation.

High-resolution structural-functional substrate-trigger characterization: Future roadmap for catheter ablation of ventricular tachycardia

Introduction

Patients with ventricular tachyarrhythmias (VT) are at high risk of sudden cardiac death. When appropriate, catheter ablation is modestly effective, with relatively high VT recurrence and complication rates. Personalized models that incorporate imaging and computational approaches have advanced VT management. However, 3D patient-specific functional electrical information is typically not considered. We hypothesize that incorporating non-invasive 3D electrical and structural characterization in a patient-specific model improves VT-substrate recognition and ablation targeting.

Materials and methods

In a 53-year-old male with ischemic cardiomyopathy and recurrent monomorphic VT, we built a structural-functional model based on high-resolution 3D late-gadolinium enhancement (LGE) cardiac magnetic resonance imaging (3D-LGE CMR), multi-detector computed tomography (CT), and electrocardiographic imaging (ECGI). Invasive data from high-density contact and pace mapping obtained during endocardial VT-substrate modification were also incorporated. The integrated 3D electro-anatomic model was analyzed off-line.

Results

Merging the invasive voltage maps and 3D-LGE CMR endocardial geometry led to a mean Euclidean node-to-node distance of 5 ± 2 mm. Inferolateral and apical areas of low bipolar voltage (<1.5 mV) were associated with high 3D-LGE CMR signal intensity (>0.4) and with higher transmurality of fibrosis. Areas of functional conduction delay or block (evoked delayed potentials, EDPs) were in close proximity to 3D-LGE CMR-derived heterogeneous tissue corridors. ECGI pinpointed the epicardial VT exit at ∼10 mm from the endocardial site of origin, both juxtaposed to the distal ends of two heterogeneous tissue corridors in the inferobasal left ventricle. Radiofrequency ablation at the entrances of these corridors, eliminating all EDPs, and at the VT site of origin rendered the patient non-inducible and arrhythmia-free until the present day (20 months follow-up). Off-line analysis in our model uncovered dynamic electrical instability of the LV inferolateral heterogeneous scar region which set the stage for an evolving VT circuit.

Discussion and conclusion

We developed a personalized 3D model that integrates high-resolution structural and electrical information and allows the investigation of their dynamic interaction during arrhythmia formation. This model enhances our mechanistic understanding of scar-related VT and provides an advanced, non-invasive roadmap for catheter ablation.

Best Practices for the Catheter Ablation of Ventricular Arrhythmias

Techniques for catheter ablation have evolved to effectively treat a range of ventricular arrhythmias. Pre-operative electrocardiographic and cardiac imaging data are very useful in understanding the arrhythmogenic substrate and can guide mapping and ablation. In this review, we focus on best practices for catheter ablation, with emphasis on tailoring ablation strategies, based on the presence or absence of structural heart disease, underlying clinical status, and hemodynamic stability of the ventricular arrhythmia. We discuss steps to make ablation safe and prevent complications, and techniques to improve the efficacy of ablation, including optimal use of electroanatomical mapping algorithms, energy delivery, intracardiac echocardiography, and selective use of mechanical circulatory support.

Intracardiac Electrogram Targets for Ventricular Tachycardia Ablation

The pathogenesis of ventricular tachycardia (VT) in most patients with a prior myocardial scarring is reentry involving compartmentalized muscle fibers protected within the scar. Often the 12-lead ECG morphology of the VT itself is not available when treated with a defibrillator. Consequently, VT ablation takes on an interesting challenge of finding critical targets in sinus rhythm. High-density recordings are essential to evaluate a substrate based on whole electrogram voltage and activation delay, supplemented with substrate perturbation through alternate site pacing or introducing an extra stimulation. In this article, we discuss contemporary intracardiac electrogram targets for VT ablation, with explanation on each of their specific fundamental physiology.

Automated Identification of Ventricular Tachycardia Ablation Targets: Multicenter Validation and Workflow Characterization

Decrement evoked potentials (EPs) (DeEPs) constitute an accepted method to identify physiological ventricular tachycardia (VT) ablation targets without inducing VT. The feasibility of automated software (SW) in the detection of arrhythmogenic VT substrate has been documented. However, multicenter validation of automated SW and workflow has yet to be characterized. The objective of this study was to describe the functionality of a novel DeEP SW (Biosense Webster, Diamond Bar, CA, USA) and evaluate the independent performance of the automated algorithm using multicenter data. VT ablation cases were performed in the catheterization laboratory and retrospectively analyzed using the DeEP SW. The algorithm indicated and mapped DeEPs by first identifying capture in surface electrocardiograms (ECGs). Once capture was confirmed, the EPs of S1 paces were detected. The algorithm checked for the stability of S1 EPs by comparing the last 3 of the 8 morphologies and attributing standard deviation values. The extra-stimulus EP was then detected by comparing it to the S1 EP. Once detected, the DeEP value was computed from the extra-stimulus and displayed as a sphere on a voltage map. A total of 5,885 DeEP signals were extracted from 21 substrate mapping cases conducted at 3 different centers (in Spain, Canada, and Australia). A gold standard was established from ECGs manually marked by subject experts. Once the algorithm was deployed, 91.6% of S2 algorithm markings coincided with the gold standard, 1.9% were false-positives, and 0.1% were false-negatives. Also, 6.4% were non-specific DeEP detections. In conclusion, the automated DeEP algorithm identifies and displays DeEP points, revealing VT substrates in a multicenter validation study. The automation of identification and mapping display is expected to improve efficiency.

Ventricular Tachycardia Ablation Guided by Functional Substrate Mapping: Practices and Outcomes

Catheter ablation of ventricular tachycardia has demonstrated its important role in the treatment of ventricular tachycardia in patients with structural cardiomyopathy. Conventional mapping techniques used to define the critical isthmus, such as activation mapping and entrainment, are limited by the non-inducibility of the clinical tachycardia or its poor hemodynamic tolerance. To overcome these limitations, a voltage mapping strategy based on bipolar electrograms peak to peak analysis was developed, but a low specificity (30%) for VT isthmus has been described with this approach. Functional mapping strategy relies on the analysis of the characteristics of the electrograms but also their propagation patterns and their response to extra-stimulus or alternative pacing wavefronts to define the targets for ablation. With this review, we aim to summarize the different functional mapping strategies described to date to identify ventricular arrhythmic substrate in patients with structural heart disease.

Substrate-based approaches in ventricular tachycardia ablation

Catheter ablation for ventricular tachycardia (VT) in patients with structural heart disease is now part of standard care. Mapping and ablation of the clinical VT is often limited when the VT is noninducible, nonsustained or not haemodynamically tolerated. Substrate-based ablation strategies have been developed in an aim to treat VT in this setting and, subsequently, have been shown to improve outcomes in VT ablation when compared to focused ablation of mapped VTs. Since the initial description of linear ablation lines targeting ventricular scar, many different approaches to substrate-based VT ablation have been developed. Strategies can broadly be divided into three categories: 1) targeting abnormal electrograms, 2) anatomical targeting of conduction channels between areas of myocardial scar, and 3) targeting areas of slow and/or decremental conduction, identified with “functional” substrate mapping techniques. This review summarises contemporary substrate-based ablation strategies, along with their strengths and weaknesses.

Contemporary Management of Complex Ventricular Arrhythmias

Percutaneous catheter ablation is an effective and safe therapy that can eliminate ventricular tachycardia, reducing the risks of both recurrent arrhythmia and shock therapies from a defibrillator. Successful ablation requires accurate identification of arrhythmic substrate and the effective delivery of energy to the targeted tissue. A thorough pre-procedural assessment is needed before considered 3D electroanatomical mapping can be performed. In contemporary practice, this must combine traditional electrophysiological techniques, such as activation and entrainment mapping, with more novel physiological mapping techniques for which there is an ever-increasing evidence base. Novel techniques to maximise energy delivery to the tissue must also be considered and balanced against their associated risks of complication. This review provides a comprehensive appraisal of contemporary practice and the evidence base that supports recent developments in mapping and ablation, while also considering potential future developments in the field.

Application of EnsiteTM LiveView Function for Identification of Scar-related Ventricular Tachycardia Isthmus

INTRODUCTION

Dynamic display of real-time wavefront activation pattern may facilitate the recognition of reentrant circuits, particularly the diastolic path of ventricular tachycardia (VT).

OBJECTIVE

We aimed to evaluate the feasibility of LiveView Dynamic Display for mapping the critical isthmus of scar-related reentrant VT.

METHODS

Patients with mappable scar-related reentrant VT were selected. The characteristics of the underlying substrates and VT circuits were assessed using HD grid multi-electrode catheter. The VT isthmuses were identified based on the activation map, entrainment, and ablation results. The accuracy of the LiveView findings in detecting potential VT isthmus was assessed.

RESULTS

We studied 18 scar-related reentrant VTs in 10 patients (median age: 59.5 years, 100% male) including 6 and 4 patients with ischemic and non-ischemic cardiomyopathy, respectively. The median VT cycle length was 426 ms (interquartile range: 386-466 ms). Among 590 regional mapping displays, 92.0% of the VT isthmus sites were identified by LiveView Dynamic Display. The accuracy of LiveView for isthmus identification was 84%, with positive and negative predictive values of 54.8% and 97.8%, respectively. The area with abnormal electrograms was negatively correlated with the accuracy of LiveView Dynamic Display (r = -0.506, p = 0.027). The median time interval to identify a VT isthmus using LiveView was significantly shorter than that using conventional activation maps (50.5 [29.8-120] vs. 219 [157.5-400.8] s, p = 0.015).

CONCLUSION

This study demonstrated the feasibility of LiveView Dynamic Display in identifying the critical isthmus of scar-related VT with modest accuracy. This article is protected by copyright. All rights reserved.

[Update on ablation of ventricular tachyarrhythmias]

Catheter ablation of ventricular tachycardia (VT) is performed with increasing frequency in clinical practice. Whereas the reported success rates of idiopathic VT are high, catheter ablation of VT in patients with structural heart disease with its scar-related re-entry mechanism may remain a challenge especially if deep intramyocardial or epicardial portions exist. The integration of modern cardiac imaging, new functional mapping strategies and catheter technologies allow optimized identification and characterization of the critical arrhythmogenic substrate and hence a more targeted VT ablation. The extent to which these innovations will have the potential to improve VT ablation success rates will be determined by future studies.

Structure and function of the ventricular tachycardia isthmus

Catheter ablation of postinfarction reentrant ventricular tachycardia (VT) has received renewed interest owing to the increased availability of high-resolution electroanatomic mapping systems that can describe the VT circuits in greater detail, and the emergence and need to target noninvasive external beam radioablation. These recent advancements provide optimism for improving the clinical outcome of VT ablation in patients with postinfarction and potentially other scar-related VTs. The combination of analyses gleaned from studies in swine and canine models of postinfarction reentrant VT, and in human studies, suggests the existence of common electroanatomic properties for reentrant VT circuits. Characterizing these properties may be useful for increasing the specificity of substrate mapping techniques and for noninvasive identification to guide ablation. Herein, we describe properties of reentrant VT circuits that may assist in elucidating the mechanisms of onset and maintenance, as well as a means to localize and delineate optimal catheter ablation targets.

Multiparametric analysis of geometric features of fibrotic textures leading to cardiac arrhythmias

One of the important questions in cardiac electrophysiology is to characterise the arrhythmogenic substrate; for example, from the texture of the cardiac fibrosis, which is considered one of the major arrhythmogenic conditions. In this paper, we perform an extensive in silico study of the relationships between various local geometric characteristics of fibrosis on the onset of cardiac arrhythmias. In order to define which texture characteristics have better predictive value, we induce arrhythmias by external stimulation, selecting 4363 textures in which arrhythmia can be induced and also selecting 4363 non-arrhythmogenic textures. For each texture, we determine such characteristics as cluster area, solidity, mean distance, local density and zig-zag propagation path, and compare them in arrhythmogenic and non-arrhythmogenic cases. Our study shows that geometrical characteristics, such as cluster area or solidity, turn out to be the most important for prediction of the arrhythmogenic textures. Overall, we were able to achieve an accuracy of 67% for the arrhythmogenic texture-classification problem. However, the accuracy of predictions depends on the size of the region chosen for the analysis. The optimal size for the local areas of the tissue was of the order of 0.28 of the wavelength of the arrhythmia. We discuss further developments and possible applications of this method for characterising the substrate of arrhythmias in fibrotic textures.

Maximizing detection and optimal characterization of local abnormal ventricular activity in nonischemic cardiomyopathy: LAVAMAX & LAVAFLOW

Background

Sites of local abnormal ventricular activation (LAVA) are ventricular tachycardia (VT) ablation targets. In nonischemic cardiomyopathy (NICM), minute and sparse LAVA potentials are mapped with difficulty with direction-sensitive bipolar electrograms (EGM). A method for its optimal characterization independent of electrode orientation has not been explored.

Objective

Maximize voltages and calculate overall activation direction at LAVA sites, independent of catheter and wave direction, using omnipolar technology (OT) in NICM.

Methods

Four diseased isolated human hearts from NICM patients were mapped epicardially using a high-density grid. Bipolar EGMs with at least 2 activation segments separated by at least 25 ms were identified. We used OT to maximize voltages (LAVA_MAX) and measured overall wave direction (LAVA_FLOW) for both segments. Clinically relevant voltage proportion (CRVP) was used to estimate the proportion of directionally corrected bipoles. Concordance and changes in direction vectors were measured via mean vector length and angular change.

Results

OT provides maximal LAVA voltages (OT: 0.83 ± 0.09 mV vs Bi: 0.61 ± 0.06 mV, P < .05) compared to bipolar EGMs. OT optimizes LAVA voltages, with 32% (CRVP) of LAVA bipoles directionally corrected by OT. OT direction vectors at LAVA sites demonstrate general concordance, with an average of 62% ± 5%. A total of 72% of direction vectors change by more than 35° at LAVA sites.

Conclusion

The omnipolar mapping approach allows maximizing voltage and determining the overall direction of wavefront activity at LAVA sites in NICM.

Limitations and Pitfalls of Substrate Mapping for Ventricular Tachycardia

The fundamental hypothesis of substrate mapping for scar-mediated ventricular tachycardia is that surrogates of the isthmus can be identified and targeted with ablation during sinus rhythm. These surrogates include electrocardiographic indications for electric discontinuity such as fractionation, split, late, and long potentials, also evident as sites displaying activation slowing. However, ablation strategies targeting these surrogates during sinus rhythm have resulted in unacceptably high rates of clinical failures, promoting the idea that a more widespread ablation may be required. High-resolution mapping technologies provide an opportunity to examine the substrate at greater detail; however, their use has not yet translated into improved clinical outcomes. This may be related to ongoing efforts to examine the same surrogates at higher resolution instead of using high-resolution technologies for discovering new and potentially more specific surrogates. This article reviews common limitations and pitfalls of substrate mapping and discusses new opportunities for high-resolution mapping to increase the accuracy of substrate mapping: 1) multielectrode mapping catheters provide an opportunity to rapidly examine the substrate during electrophysiological conditions that more closely simulate ventricular tachycardia by means of activation from different directions and coupling intervals; 2) electrogram annotation methods based on the maximal negative derivative of the extracellular potential or maximal voltage are often inaccurate in nonuniform anisotropic tissue. The use of multielectrode catheters may improve the accuracy of electrogram annotation by using spatiotemporal dispersion of single-beat acquisitions and a localized indifferent reference; and 3) resetting and entrainment remain important methods for studying re-entry for and guiding ablation.

Minimising radiation exposure in catheter ablation of ventricular arrhythmias

Background

Conventional fluoroscopy guided catheter ablation (CA) is an established treatment option for ventricular arrhythmias (VAs). However, with the complex nature of most procedures, patients and staff bare an increased radiation exposure. Near-zero or zero-fluoroscopy CA is an alternative method which could substantially reduce or even eliminate the radiation dose. Our aim was to analyse procedural outcomes with fluoroscopy minimising approach for treatment of VAs in patients with structurally normal hearts (SNH) and structural heart disease (SHD).

Methods

Fifty-two (age 53.4 ± 17.8 years, 38 male, 14 female) consecutive patients who underwent CA of VAs in our institution between May 2018 and December 2019 were included. Procedures were performed primarily with the aid of the three-dimensional electro-anatomical mapping system and intra-cardiac echocardiography. Fluoroscopy was considered only in left ventricular (LV) summit mapping for coronary angiography and when epicardial approach was planned. Acute and long-term procedural outcomes were analysed.

Results

Sixty CA procedures were performed. Twenty-five patients had SHD-related VAs (Group 1) and 27 patients had SNH (Group 2). While Group 1 had significantly higher total procedural time (256.9 ± 71.7 vs 123.6 ± 42.2 min; p < 0.001) compared to Group 2, overall procedural success rate [77.4% (24/31) vs 89.7% (26/29); p = 0.20)] and recurrence rate after the first procedure [8/25, (32%) vs 8/27, (29.6%); p = 0.85] were similar in both groups. Fluoroscopy was used in 3 procedures in Group 1 where epicardial approach was needed and in 4 procedures in Group 2 where LV summit VAs were ablated. Overall procedure-related major complication rate was 5%.

Conclusions

Fluoroscopy minimising approach for CA of VAs is feasible and safe in patients with SHD and SNH. Fluoroscopy could not be completely abolished in VAs with epicardial and LV summit substrate location.

Dynamic High-density Functional Substrate Mapping Improves Outcomes in Ischaemic Ventricular Tachycardia Ablation: Sense Protocol Functional Substrate Mapping and Other Functional Mapping Techniques

Post-infarct-related ventricular tachycardia (VT) occurs due to reentry over surviving fibres within ventricular scar tissue. The mapping and ablation of patients in VT remains a challenge when VT is poorly tolerated and in cases in which VT is non-sustained or not inducible. Conventional substrate mapping techniques are limited by the ambiguity of substrate characterisation methods and the variety of mapping tools, which may record signals differently based on their bipolar spacing and electrode size. Real world data suggest that outcomes from VT ablation remain poor in terms of freedom from recurrent therapy using conventional techniques. Functional substrate mapping techniques, such as single extrastimulus protocol mapping, identify regions of unmasked delayed potentials, which, by nature of their dynamic and functional components, may play a critical role in sustaining VT. These methods may improve substrate mapping of VT, potentially making ablation safer and more reproducible, and thereby improving the outcomes. Further large-scale studies are needed.

High-Resolution Measurement of Local Activation Time Differences From Bipolar Electrogram Amplitude

Localized changes in myocardial conduction velocity (CV) are pro-arrhythmic, but high-resolution mapping of local CV is not yet possible during clinical electrophysiology procedures. This is in part because measurement of local CV at small spatial scales (1 mm) requires accurate annotation of local activation time (LAT) differences with very high temporal resolution (≤1 ms), beyond that of standard clinical methods. We sought to develop a method for high-resolution measurement of LAT differences and validate against existing techniques. First, we use a simplified theoretical model to identify a quantitative relationship between the LAT difference of a pair of electrodes and the peak amplitude of the bipolar EGM measured between them. This allows LAT differences to be calculated from bipolar EGM peak amplitude, by a novel "Determination of EGM Latencies by Transformation of Amplitude" (DELTA) method. Next, we use simulated EGMs from a computational model to validate this method. With 1 kHz sampling, LAT differences less than 4 ms were more accurately measured with DELTA than by standard LAT annotation (mean error 3.8% vs. 22.9%). In a 1-dimensional and a 2-dimension model, CV calculations were more accurate using LAT differences found by the DELTA method than by standard LAT annotation (by unipolar dV/dt timing). DELTA-derived LAT differences were more accurate than standard LAT annotation in simulated complex fractionated EGMs from a model incorporating fibrosis. Finally, we validated the DELTA method in vivo using 18,740 bipolar EGMs recorded from the left atrium of 10 atrial fibrillation patients undergoing catheter ablation. Using clinical EGMs, there was agreement in LAT differences found by DELTA, standard LAT annotation, and unipolar waveform cross-correlation. These results demonstrate an underlying relationship between a bipolar EGM's peak amplitude and the activation time difference between its two electrodes. Our computational modeling and clinical results suggest this relationship can be leveraged clinically to improve measurement accuracy for small LAT differences, which may improve CV measurement at small spatial scales.

Updates in Ventricular Tachycardia Ablation

Sudden cardiac death (SCD) due to recurrent ventricular tachycardia is an important clinical sequela in patients with structural heart disease. As a result, ventricular tachycardia (VT) has emerged as a major clinical and public health problem. The mechanism of VT is predominantly mediated by re-entry in the presence of arrhythmogenic substrate (scar), though focal mechanisms are also important. Catheter ablation for VT, when compared to standard medical therapy, has been shown to improve VT-free survival and burden of device therapies. Approaches to VT ablation are dependent on the underlying disease process, broadly classified into idiopathic (no structural heart disease) or structural heart disease (ischemic or non-ischemic heart disease). This update aims to review recent advances made for the treatment of VT ablation, with respect to current clinical trials, peri-procedure risk assessments, pre-procedural cardiac imaging, electro-anatomic mapping and advances in catheter and non-catheter based ablation techniques.

Close-coupled pacing to identify the "functional" substrate of ventricular tachycardia: Long-term outcomes of the paced electrogram feature analysis technique

BACKGROUND

The conduction delay and block that compose the critical isthmus of macroreentrant ventricular tachycardia (VT) is partly "functional" in that they only occur at faster cycle lengths. Close-coupled pacing stresses the myocardium's conduction capacity and may reveal late potentials (LPs) and fractionation. Interest has emerged in targeting this functional substrate.

OBJECTIVE

The purpose of this study was to assess the feasibility and efficacy of a functional substrate VT ablation strategy.

METHODS

Patients with scar-related VT undergoing their first ablation were recruited. A closely coupled extrastimulus (ventricular effective refractory period + 30 ms) was delivered at the right ventricular apex while mapping with a high-density catheter. Sites of functional impaired conduction exhibited increased electrogram duration due to LPs/fractionation. The time to last deflection was annotated on an electroanatomic map, readily identifying ablation targets.

RESULTS

A total of 40 patients were recruited (34 [85%] ischemic). Median procedure duration was 330 minutes (interquartile range [IQR] 300-369), and ablation time was 49.4 minutes (IQR 33.8-48.3). Median functional substrate area was 41.9 cm² (IQR 22.1-73.9). It was similarly distributed across bipolar voltage zones. Noninducibility was achieved in 34 of 40 patients (85%). Median follow-up was 711 days (IQR 255.5-972.8), during which 35 of 39 patients (89.7%) did not have VT recurrence, and 3 of 39 (7.5%) died. Antiarrhythmic drugs were continued in 53.8% (21/39).

CONCLUSION

Functional substrate ablation resulted in high rates of noninducibility and freedom from VT. Mapping times were increased considerably. Our findings add to the encouraging trend reported by related techniques. Randomized multicenter trials are warranted to assess this next phase of VT ablation.

Decrement Evoked Potential Mapping to Guide Ventricular Tachycardia Ablation: Elucidating the Functional Substrate

Empirical approaches to targeting the ventricular tachycardia (VT) substrate include mapping of late potentials, local abnormal electrogram, pace-mapping and homogenisation of the abnormal signals. These approaches do not try to differentiate between the passive or active role of local signals as the critical components of the VT circuit. By not considering the functional components, these approaches often view the substrate as a fixed anatomical barrier. Strategies to improve the success of VT ablation need to include the identification of critical functional substrate. Decrement-evoked potential (DeEP) mapping has been developed to elucidate this using an extra-stimulus added to a pacing drive train. With knowledge translation in mind, the authors detail the evolution of the DeEP concept by way of a study of simultaneous panoramic endocardial mapping in VT ablation; an in silico modelling study to demonstrate the factors influencing DeEPs; a multicentre VT ablation validation study; a practical approach to DeEP mapping; the potential utility of DeEPs to identify arrhythmogenic atrial substrate; and, finally, other functional mapping strategies.

Impact of Micro-, Mini- and Multi-Electrode Mapping on Ventricular Substrate Characterisation

Accurate substrate characterisation may improve the evolving understanding and treatment of cardiac arrhythmias. During substrate-based ablation techniques, wide practice variations exist with mapping via dedicated multi-electrode catheter or conventional ablation catheters. Recently, newer ablation catheter technology with embedded mapping electrodes have been introduced. This article focuses on the general misconceptions of voltage mapping and more specific differences in unipolar and bipolar signal morphology, field of view, signal-to-noise ratio, mapping capabilities (density and resolution), catheter-specific voltage thresholds and impact of micro-, mini- and multi-electrodes for substrate mapping. Efficiency and cost-effectiveness of different catheter types are discussed. Increasing sampling density with smaller electrodes allows for higher resolution with a greater likelihood to record near-field electrical information. These advances may help to further improve our mechanistic understanding of the correlation between substrate and ventricular tachycardia, as well as macro-reentry arrhythmia in humans.

Multicenter Study of Dynamic High-Density Functional Substrate Mapping Improves Identification of Substrate Targets for Ischemic Ventricular Tachycardia Ablation

OBJECTIVES

The goal of this study was to evaluate the role of dynamic substrate changes in facilitating conduction delay and re-entry in ventricular tachycardia (VT) circuits.

BACKGROUND

The presence of dynamic substrate changes facilitate functional block and re-entry in VT but are rarely studied as part of clinical VT mapping.

METHODS

Thirty patients (age 67 ± 9 years; 27 male subjects) underwent ablation. Mapping was performed with the Advisor HD Grid multipolar catheter. A bipolar voltage map was obtained during sinus rhythm (SR) and right ventricular sense protocol (SP) single extra pacing. SR and SP maps of late potentials (LP) and local abnormal ventricular activity (LAVA) were made and compared with critical sites for ablation, defined as sites of best entrainment or pace mapping. Ablation was then performed to critical sites, and LP/LAVA identified by the SP.

RESULTS

At a median follow-up of 12 months, 90% of patients were free from antitachycardia pacing (ATP) or implantable cardioverter-defibrillator shocks. SP pacing resulted in a larger area of LP identified for ablation (19.3 mm² vs. 6.4 mm²) during SR mapping (p = 0.001), with a sensitivity of 87% and a specificity of 96%, compared with 78% and 65%, respectively, in SR.

CONCLUSIONS

LP and LAVA observed during the SP were able to identify regions critical for ablation in VT with a greater accuracy than SR mapping. This may improve substrate characterization in VT ablation. The combination of ablation to critical sites and SP-derived LP/LAVA requires further assessment in a randomized comparator study.

Signature signal strategy: Electrogram-based ventricular tachycardia mapping

Multiple decades of work have recognized complexities of substrates responsible for ventricular tachycardia (VT). There is sufficient evidence that 3 critical components of a re-entrant VT circuit, namely, region of slow conduction, zone of unidirectional block, and exit site, are located in spatial vicinity to each other in the ventricular scar. Each of these components expresses characteristic electrograms in sinus rhythm, at initiation of VT, and during VT, respectively. Despite this, abnormal electrograms are widely targeted without appreciation of these signature electrograms during contemporary VT ablation. Our aim is to stimulate physiology-based VT mapping and a targeted ablation of VT. In this article, we focus on these 3 underappreciated aspects of the physiology of ischemic scar-related VT circuits that have practical applications during a VT ablation procedure. We explore the anatomic and functional elements underlying these distinctive bipolar electrograms, specifically the contribution of tissue branching, conduction restitution, and wave curvature to the substrate, as they pertain to initiation and maintenance of VT. We propose a VT ablation approach based on these 3 electrogram features that can be a potential practical means to recognize critical elements of a VT circuit and target ablation.

Electrogram recording and analyzing techniques to optimize selection of target sites for ablation of cardiac arrhythmias

The extracellular electrogram is caused by transmembrane currents that flow into extracellular space during propagation of the electrical impulse. Electrograms are usually recorded in unipolar or bipolar mode that have different characteristics, but provide complementary information. Both recording modes have specific advantages, but also suffer from disadvantages. Techniques to circumvent some of the weaknesses are reviewed. The origin of remote and fractionated deflections and their relation with electrode characteristics are discussed. Epicardial and endocardial sites of origin and breakthrough sites as well as the effect of fatty tissue on extracellular electrograms are presented. Induction of tachycardia to assess the arrhythmogenic area is not always possible because of hemodynamic instability of the patient. Techniques to assess sites with high reentry vulnerability without induction of arrhythmias are outlined such as activation‐repolarization mapping and decremental stimulation. Pitfalls of substrate mapping and techniques to avoid them as omnipolar mapping and characterization of complex electrograms by entropy are presented. Technical aspects that influence electrogram morphology as electrode size, filtering, contact force, and catheter position are delineated. Data from the various publications suggest that a combination of unipolar and bipolar electrogram analysis techniques is helpful to optimize determination of target sites for ablation.

Mapping and Ablation of Unmappable Ventricular Tachycardia, Ventricular Tachycardia Storm, and Those in Acute Myocardial Infarction

In stable ventricular tachycardia (VT), activation mapping and entrainment mapping are the most important strategies to describe the reentrant circuit and its critical components. In many patients, however, VT is noninducible or hemodynamically unstable and unmappable. Several technological advances have broadened ablation options in unmappable VTs. Preprocedural imaging and intraprocedural imaging play an important role in location and extent of the substrate. Electroanatomic mapping with several technological improvements allows more precise electrical assessment of the substrate. A combination of imaging and electroanatomic mapping allows substantial modification of arrhythmogenic substrate in sinus rhythm or during device pacing without hemodynamic compromise.